Added Cookbook link to the navbar
Added Cookbook link to the navbar

For easy access to a very used section. Removed the citation link from
navbar because we already have that below anyway.

cmeessen/fatiando,santis19/fatiando,mtb-za/fatiando,fatiando/fatiando,victortxa/fatiando,cmeessen/fatiando,eusoubrasileiro/fatiando,eusoubrasileiro/fatiando_seismic,eusoubrasileiro/fatiando,drandykass/fatiando,mtb-za/fatiando,fatiando/fatiando,rafaelmds/fatiando,victortxa/fatiando,santis19/fatiando,eusoubrasileiro/fatiando_seismic,rafaelmds/fatiando,drandykass/fatiando,eusoubrasileiro/fatiando